Specifies what nested things a visitor wants to visit. By “nested things”, we are referring to bits of HIR that are not directly embedded within one another but rather indirectly, through a table in the crate. This is done to control dependencies during incremental compilation: the non-inline bits of HIR can be tracked and hashed separately.
The most common choice is
OnlyBodies, which will cause the visitor to
visit fn bodies for fns that it encounters, and closure bodies, but
skip over nested item-like things.
See the comments at
rustc_hir::intravisit for more details on the overall